The present invention relates to multiplexers, and in particular, to a multiplexer architecture for detecting leakage currents between input channels.
A multiplexer is a device that provides an output selected from a plurality of inputs. Multiplexers are beneficial because they allow more expensive resources (such as analog-to-digital converters) to be shared by a plurality of devices. In this way, rather than employ a separate analog-to-digital converter for each device, a single analog-to-digital converter may be employed for a plurality of devices.
A plurality of switches (e.g., metal-oxide semiconductor devices, opto-couplers, etc.) employed by the multiplexer are controlled (i.e., opened and closed) to select the desired input (i.e., channel) to provide at the output of the multiplexer. Ideally, the switches when open provide total isolation between each of the plurality of channels. In actuality, even when open the switches allow small amounts of current to leak between channels. This undesirable current is referred to as ‘leakage current’, the result of which can have a negative impact on the integrity of the signal provided at the output of the multiplexer.
In many applications, leakage currents are insubstantial and do not significantly affect the integrity of the multiplexer output. However, factors such as temperature and device-to-device potentials (i.e., input devices of the multiplexer being maintained, either intentionally or unintentionally at significantly different potentials), either alone or in combination, increase the leakage current associated with switches employed by the multiplexer.
In many applications (such as process control applications), even a small change in the integrity of the signal provided by the multiplexer may result in significant application errors. It would therefore be beneficial to detect the presence of leakage currents and/or compensate the output signal provided by the multiplexer in response to detected leakage currents.